MOS - If diesels are the root of all air quality issues, why does urban air quality not improve (and often deteriorates) on weekends when diesel truck traffic decreases by as much as 80% and NOx decreases by as much as 50% (weekend ozone effect)?

As I mentioned in an earlier post, even "Bin 10" diesels are closer to "PZEV" with respect to VOCs (NMHCs) than even the gasoline cars classified as PZEV if you include the evaporative emissions during refueling and distribution of highly volatile gasoline.

VOCs decompose in the atmosphere to fine particles (SOA) and formaldehyde, not to mention their role in ozone (smog) formation.

I commend you for going from a 20 mpg vehicle to a 50 mpg hybrid and I acknowledge that there are some disadvantages to diesels (e.g., fuel not available at every gas station). However, I strongly disagree with your "diesels are dirty" assertion, especially with respect to the current generation of diesel vehicles.